WhatsApp currently has about 450 million active monthly users, and among those, 320 million who log into the app daily, the company said Wednesday, after Facebook announced its purchase plans. In 2012, the South China Morning Post reported that WhatsApp was used by about 45% of the people in Hong Kong.

In the overcrowded world of messaging apps, there are a few things that make WhatsApp stand out aside from its gigantic user base: It doesn’t place ads in its apps, and doesn’t build any additional services—such as games, location services or retail—on top of the basic messaging component.

Instead, WhatsApp makes money by charging users $1 per year to use its service. WhatsApp said the Facebook deal will allow it to continue to operate as a standalone business and that nothing would change for users.

Asian rivals Line, Kakao Talk and WeChat are free, but tend to use a messaging component as the foundation of a social network of games and other revenue-generating services.

Here’s a rundown of WhatsApp’s competition in the U.S. and around the globe:

Line
Developed by a Japanese subsidiary of Korean Internet portal operator Naver, Line offers text messaging, voice calls as well as photo-sharing, games and digital comic books. It also generates revenues through the sales of stickers that users can include in chats with friends.

Launched in 2011, Line is free to download and is popular in Japan, Taiwan and Thailand. Line has more than 340 million registered users (which is different—and generally much higher—than monthly active users). The company said its revenue for the fourth quarter of last year jumped more than fivefold to ¥12.2 billion ($120 million) from ¥2.2 billion a year earlier. The bulk of its revenue comes from videogames that users download for free but then make in-game purchases.

Kakao Talk
South Korea’s Kakao Talk, which was launched in 2010, has 133 million registered users. Like many of its Asia rivals, Kakao Talk is free to download and has branched out into games, a mobile reader and e-commerce. It has struggled to grow beyond Korea’s home market. Parent company Kakao Inc. is said to be planning an initial public offering that would value the company at more than $2 billion. The IPO funds would be used to fuel expansion into new markets.

WeChat
In China, the dominant messaging app is Tencent Holdings’ WeChat. It’s free to download and it now has 272 million monthly active users in China and abroad, according to the company. The majority of its users are in China, although the company is pushing hard to expand abroad. WeChat was launched in late 2010. Last year, it spent $200 million on overseas ad campaigns to push WeChat into many markets including India, South Africa, Spain and Italy.

iMessage
Apple’s iMessage allows iPhone users to send text messages to each other without having to pay an SMS fee to a carrier. In addition, iPad, iPod Touch and Mac users can send messages to other Apple users through iMessage. The service is free, but it’s limited to only Apple devices, and users need to register with Apple. Apple does not disclose the number of iMessage users.

BBM
BBM—formerly known as BlackBerry Messenger—was once a killer app for the popular business-first smartphones, allowing forprivate messaging between BlackBerry owners. But when BlackBerry handsets began to fall out of favor, BBM was released on other platforms. The shift was successful: The service currently has about 80 million active monthly users, 20 million of which are accessing the app on iOS and Android. As the user base has grown—particularly in Europe and Indonesia—so too have the capabilities of the app. BBM can now be used to for group chats, photo and emoticon messaging and even voice calls.

Facebook Messenger
Though Facebook is now set to buy WhatsApp (pending regulatory approval), it already has a couple of messaging services of itsown. Facebook Messenger, found on the social network’s website and apps, allows for private and group messaging. The company doesn’t specify how many Facebook users are on messaging daily, but it’s likely that it’s just a fraction of the network’s 1.2 billion users.

Snapchat
Snapchat, the messaging app that allows users to send each other private, self-destructing photos and video, is most popular in the U.S. As of November, it handled 400 million disappearing messages per day. But while the company is considered a leader in the messaging app space, it has never disclosed just how many users it has. In December, the company famous for denying Facebook’s $3 billion overture raised an investment of $50 million, at least some of which is going toward building up its 15-person engineering team.